The present invention relates to communications, and more particularly, to data communications networks and terminals.
As digital communications networks become more advanced, chip and equipment makers continue to improve and advance devices, methods and systems used to facilitate higher and higher data transfer rates using smaller and less costly equipment and devices.
In particular, a media independent interface (MII) specification may allow a media access control (MAC) layer device (a MAC device) to control and interact with a physical interface (PHY) layer device (a PHY device), depending on the type of physical media being controlled by the PHY layer. Moreover, Cisco Systems, Inc. has developed improvements to MII specification defined by the Serial-MII (“SMII”) specification.
SMII specifies that instead of using a conventional seven-wire arrangement to transfer Ethernet data between a MAC device and a corresponding PHY device, time division multiplexing (“TDM”) techniques can be used to transport the same amount of data over two wires serially. This is accomplished by using a global clock signal to provide timing to a plurality of MAC devices and corresponding PHY devices. In addition, a global sync signal is sent to the MAC and PHY devices. Thus, each group of components (typically comprising eight MAC/PHY device pairs) may only need 4 pins/wires instead of the nine per MAC/PHY device pair used in conventional Ethernet systems.
While fewer pins and wires are required to connect corresponding MAC and PHY devices under the SMII specification, the MAC and PHY devices may be inherently required to be located proximate one another (e.g., within approximately 1.5 ns) due to trace delay caused by propagation characteristics of the connecting medium (e.g., copper). In other words, using SMII, corresponding MAC and PHY devices may realistically need to be located on the same card (e.g., printed circuit board or “PCB”). Application of SMII systems may be useful in computer network systems, telephony systems or any other type of system that transmits and receives digital data using the Ethernet format.
Remotely located MAC and PHY devices are discussed, for example, in U.S. Pat. No. 7,639,655 to Boine entitled “Ethernet Switch Interface For Use In Optical Nodes.” More particularly, Boine discusses MAC layer ports communicating with an equal number of PHY layer interface ports serially using SMII technology, with the MAC layer connected to the PHY layer via fiber links. A separate link is used for each direction of traffic data flow, and information data is encoded along with a frame sync signal and a clock signal into a serial stream for transmission across the network. The serial stream is decoded at the other end, and the frame sync signal is extracted to provide timing functionality. This allows full duplex operation with the MAC layer separated from the PHY layer at distances greater than a few inches. More particularly, a MAC layer may generate multiple transport links that are encoded and multiplexed into a serial signal that is transmitted over an optical network.
Notwithstanding network structures discussed above, there continues to exist a need for improved data networks, elements, and methods.